1. Field of the Invention
This invention relates to a filter circuit for filtering a high frequency signal of the microwave band or the millimeter wave band.
2. Description of the Prior Art
A filter including resonators on a printed circuit board contained in a metal box for filtering an input signal of the microwave band or the millimeter wave band through the resonators is known. Such a prior art filter is disclosed in Japanese patent application provisional publication No. 7-202507. FIG. 11 is a plan view, partially cross-sectional view, of this prior art filter. An input signal is transferred by resonators 1a top 1c on a substrate 2 contained in a box to output the filtered signal. A radio wave absorbing material 9 is provided on the inside walls of the case 8 to suppress disturbance in electromagnetic mode and to suppress generation of harmonics to reduce noise.